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    <p>Your pointer arithmetic is faulty. Adding 1 to a pointer does not advance it by one byte, but to the next element; by the size of the pointed type.</p> <p>If you have</p> <pre><code>struct foo { ... }; struct bar { ... }; struct baz { ... }; struct header { ... struct foo *foo; struct bar *bar; struct baz *baz; ... }; </code></pre> <p>you can allocate the structures using a single memory block using</p> <pre><code>struct header *ptr; ptr = malloc (sizeof (struct header) + sizeof (struct foo) + sizeof (struct bar) + sizeof (struct baz)); if (!ptr) { /* out of memory */ exit(1); } ptr-&gt;foo = (struct foo *)(ptr + 1); ptr-&gt;bar = (struct bar *)(ptr-&gt;foo + 1); ptr-&gt;baz = (struct baz *)(ptr-&gt;bar + 1); </code></pre> <p>Alternatively, if you wish to work with byte offsets (for example, if the sizes of the structures are dynamic -- quite legal in C99), you can use</p> <pre><code>struct header *ptr; char *tmp; tmp = malloc (sizeof (struct header) + sizeof (struct foo) + sizeof (struct bar) + sizeof (struct baz)); if (!tmp) { /* out of memory */ exit(1); } ptr = (struct header *)tmp; ptr-&gt;foo = (struct foo *)(tmp + sizeof (struct header)); ptr-&gt;bar = (struct bar *)(tmp + sizeof (struct header) + sizeof (struct foo)); ptr-&gt;baz = (struct baz *)(tmp + sizeof (struct header) + sizeof (struct foo) + sizeof (struct bar)); </code></pre> <p>In both cases the pointers in the <code>struct header</code> structure will get the same values relative to the pointer of the <code>struct header</code> itself. In the latter case, you must also remember to align the new pointers per ABI requirements, if you use arbitrary structure sizes.</p>
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    1. POC: One malloced block for multiple structs of different types
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    1. COMy bad. I wasn't very clear. When I said "no assumptions about struct members" what I meant is that they ARE valid C structs but they are defined elsewhere. I do not know their definitions. All I have access to is custom S1SizeOf(), S2SizeOf(), etc. routines. I do the mallocing, users "paste" their structs in there later. R.'s reply is closest to what I intend to do. Sorry for not being clear from the beginning. Basically the objective is to have one place and enough room and good alignment for custom types of which only sizes are known via their custom typeSizeOf() routines.
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    2. CO600 chars is not enough! Anyaway. One place, enough size and good alignment, good old C custom structs defined elsewhere, and later pasted into alotted spots within malloced buffer. I do not know WHAT they are, but I do know that they are structs. Hence the original question. To align or to not align.
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